1. Technical Field
The present invention relates to a technique for converting input image data into indexed color image data.
2. Related Art
For an image processing device (such as a scanner, a printer, a copying machine or a combined machine), a technique is known, which converts input image data (e.g., 24-bit RGB full color image data) into indexed color image data (in which each pixel that is included in the input image data is represented by an index value) using a table (that is called a palette and in which an index value is assigned to each color as a color number) in order to reduce the amount of the image data that is stored in a storage device such as a memory.
The image processing device performs predetermined image processing on the input image data on the basis of an appearance frequency distribution of colors of the pixels that are included in the input image data. A technique for generating a histogram of the colors of the pixels that are included in the input image data is known (refer to, for example, JP-A-2009-37277).
In order to generate the histogram of the input image data and perform the index conversion (including generation of the palette), it is necessary to process each of the pixels that are included in the input image data. Thus, the processing load of the image processing device is large. For example, when both the histogram generation and the index conversion (including the generation of the palette) are performed, the processing load of the image processing device is larger.